CB-5083: Disrupting Protein Homeostasis to Modulate ER Stress and Lipid Metabolism in Cancer Research

Introduction

Protein homeostasis, or proteostasis, is central to cellular function and survival, particularly in rapidly dividing cancer cells. Disrupting this delicate balance has emerged as a promising strategy for cancer therapy. CB-5083, a highly potent, selective, and orally bioavailable p97 inhibitor, has become a focal point in targeting the AAA-ATPase p97 (valosin-containing protein, VCP)—a key player in the endoplasmic reticulum-associated protein degradation (ERAD) pathway. While prior literature has thoroughly explored CB-5083’s mechanistic underpinnings in protein degradation and apoptosis (see this review), this article extends the conversation by illuminating the sophisticated interplay between proteostasis, ER stress, and lipid metabolism, integrating insights from both biochemical and cellular perspectives.

p97 AAA-ATPase: The Cornerstone of ER Protein Quality Control

The AAA-ATPase p97/VCP orchestrates the extraction and delivery of misfolded and poly-ubiquitinated proteins from the ER to the cytosol for proteasomal degradation. This tightly regulated process is essential for cellular adaptation to proteotoxic stress, which is frequently hijacked in cancer cells to buffer against oncogenic mutations and high protein synthesis demands. Disrupting p97 function impairs protein homeostasis, leading to the accumulation of toxic protein aggregates and activation of stress responses such as the unfolded protein response (UPR) and apoptosis.

Mechanism of Action of CB-5083: Selective Inhibition of the p97 ATPase

CB-5083 (SKU: B6032) achieves its specificity by targeting the second ATPase domain (D2) of p97, competitively blocking ATP binding. This inhibition is remarkably potent, with an IC50 of 15.4 nM against wild-type p97. Unlike pan-ATPase inhibitors, CB-5083 is highly selective, sparing non-target AAA-ATPases and reducing off-target cytotoxicity. Its oral bioavailability and favorable pharmacokinetic profile make it ideal for in vivo and translational studies.

Upon administration, CB-5083 halts the degradation of poly-ubiquitinated proteins, resulting in their ER accumulation. This triggers a cascade of cellular stress adaptations: the UPR is activated to restore homeostasis, but when the burden exceeds compensatory capacity, apoptotic pathways—particularly via caspase signaling—are induced. In cell-based models, CB-5083 causes dose-dependent accumulation of TCRα-GFP and poly-ubiquitinated substrates in the ER, culminating in selective cancer cell apoptosis induction.

Advanced Insights: CB-5083 and Lipid Homeostasis

Recent research has highlighted the interconnectedness of protein and lipid homeostasis within the ER. The reference study by Carrasquillo Rodríguez et al. (2024) demonstrates how ER-resident enzymes such as CTDNEP1 and its regulatory subunit NEP1R1 modulate membrane synthesis and lipid storage by regulating phosphatidic acid phosphatase (lipin 1) stability and activity. Crucially, the study underscores the role of proteasomal degradation in controlling CTDNEP1 levels—a pathway dependent on p97 activity. By inhibiting p97 with CB-5083, researchers can not only disrupt protein homeostasis but also perturb the regulation of ER lipid metabolism, providing a new dimension to the study of metabolic vulnerabilities in cancer cells.

Comparative Analysis: CB-5083 Versus Alternative Protein Degradation Pathway Inhibitors

Prior reviews, such as this primer, have catalogued the utility of CB-5083 in protein homeostasis disruption, but often through the lens of direct cytotoxicity and apoptosis. Here, we contextualize CB-5083 within the broader landscape of protein degradation inhibitors:

• Proteasome inhibitors (e.g., bortezomib) globally block proteasomal activity, leading to widespread protein accumulation but also significant toxicity due to lack of pathway specificity.
• p97 inhibitors such as CB-5083 act upstream, selectively impairing ERAD and associated processes, offering a more nuanced control over proteostasis.
• ERAD component inhibitors (targeting E3 ligases, ubiquitin-conjugating enzymes) may provide even greater specificity, but most lack the oral bioavailability and in vivo efficacy of CB-5083.

Unlike earlier summaries—see this comparative review—our article delves deeper into the metabolic and regulatory consequences of p97 inhibition, especially in the context of ER membrane and lipid homeostasis.

CB-5083 in Cancer Models: Beyond Tumor Growth Inhibition

In Vitro and In Vivo Efficacy

CB-5083 has been rigorously evaluated in both cell culture and animal models. In vitro, it induces rapid, dose-dependent accumulation of misfolded and poly-ubiquitinated proteins in human cell lines such as HEK293T, A549, and HCT116. This accumulation precipitates ER stress, UPR activation, and ultimately apoptosis via the caspase signaling pathway. In mouse xenograft models of colorectal adenocarcinoma, non-small-cell lung cancer, and multiple myeloma, oral administration of CB-5083 achieves tumor growth inhibition (TGI) of up to 63%, validating its translational potential.

Cellular Stress Adaptation and Metabolic Shifts

What sets CB-5083 apart from earlier generations of proteostasis disruptors is its capacity to reveal cell-intrinsic stress adaptation mechanisms—particularly the interplay between the UPR and lipid storage. The reference study by Carrasquillo Rodríguez et al. (2024) underscores how ER expansion and lipid droplet biogenesis are tightly linked to proteostasis. CB-5083-induced p97 inhibition may inadvertently influence these processes, shifting cellular metabolism and potentially sensitizing cancer cells to further metabolic or proteotoxic insults. Such nuanced effects are not extensively covered in systems biology overviews, which tend to focus on protein quality control in isolation.

Advanced Applications: Probing ER Stress, UPR, and Lipid Dynamics in Multiple Myeloma and Solid Tumors

CB-5083 is a valuable tool for dissecting ER-associated degradation and its consequences for both protein and lipid homeostasis. In the context of multiple myeloma research, where proteasome inhibitors are mainstay therapies, CB-5083 offers a complementary approach, uncovering resistance mechanisms and adaptive pathways. In solid tumor research, the compound enables exploration of ER stress as a vulnerability, especially in tumors with high secretory demands or altered lipid metabolism.

Furthermore, by leveraging insights from the CTDNEP1-NEP1R1-lipin 1 axis (Carrasquillo Rodríguez et al., 2024), researchers can interrogate how modulation of ER lipid synthesis and storage intersects with protein quality control. For example, CB-5083 may be used in combinatorial studies to determine whether disrupting both proteostasis and lipid homeostasis yields synergistic anti-tumor effects or reveals compensatory metabolic pathways.

Experimental Considerations

CB-5083 is supplied as a solid (molecular weight: 413.47, formula: C₂₄H₂₃N₅O₂), and is insoluble in water but highly soluble in DMSO (>20.65 mg/mL) and ethanol (>4.4 mg/mL). For optimal use, it should be stored at -20°C and protected from prolonged exposure in solution. Solubility can be enhanced with gentle warming and sonication. It is intended for research use only and not for diagnostic or clinical application.

Conclusion and Future Outlook

CB-5083 stands at the vanguard of selective p97 AAA-ATPase inhibitor development, offering not only a robust tool for inducing protein homeostasis disruption and cancer cell apoptosis, but also a unique window into the metabolic regulation of the ER. By bridging the gap between proteostasis and lipid metabolism, CB-5083 facilitates holistic interrogation of cancer cell vulnerabilities—an angle that extends well beyond prior reviews (discussed here). As our understanding of ER stress and metabolic adaptation deepens, CB-5083 is poised to underpin next-generation strategies for therapeutic intervention and mechanistic discovery in oncology and beyond.

For more information or to source high-quality research-grade CB-5083, visit the official Apexbio CB-5083 product page.